This invention relates to a method of storing natural gas. More particularly, the invention relates to storage of natural gas at near ambient temperatures using a solid adsorbent, in particular, a carbon molecular sieve.
U.S. Pat. No. 4,820,681 discloses an improved carbon molecular sieve which has a high capacity for carbon dioxide and may be characterized as hydrophobic, requires no binders, and may be carbonized in a single step.
Natural gas, being substantially methane, has a low molecular weight and it occupies a large volume per unit weight compared to liquid fuels. Thus, reducing the volume of natural gas is necessary for most practical applications of natural gas as a fuel. Methods for doing this could include (1) storage at high pressure, (2) liquefaction and storage at low temperatures, and (3) adsorption on solids. Of these methods the last is of particular interest since compact storage of natural gas at moderate pressures may be achieved, while avoiding the cryogenic temperatures needed for liquid natural gas of the high pressures needed for storage as a gas within reasonable size vessels.
Conventional activated carbons have been found to have reasonable capacity for natural gas but higher capacity is believed necessary for commercial success. Inorganic zeolites have also been tried, but found to have relatively low capacity for natural gas. Carbon molecular sieves also have been suggested for adsorption of natural gas. Improvements in the storage of natural gas have been disclosed in copending applications U.S. Ser. Nos. 07,906,995, 07/906,993 and 07/964,174.
The present inventors have found a method for increasing the packing density of carbon molecular sieves and thereby increasing the volumetric efficiency of the adsorption of natural gas. The invention relates to improvements in the suspension polymerization which provides a polymer precursor to such carbon molecular sieves. A discussion of suspension polymerization of vinylidene halides may be found, for example, in U.S. Pat. No. 4,163,090 to Dow Chemical Co.